Systems and methods herein generally relate to printers and copiers or reproduction machines, and more particularly, concern utilizing the reload operation of a developer donor roll to calibrate sensors.
In modern electrostatic printers, a complex system is utilized to transfer the marking material from a container to an intermediate device, and then finally onto the print media. For ease of nomenclature, the term “toner” as used herein is intended to represent all forms of marking materials that are patterned or transferred using an electrical and/or static charge (whether currently known or developed in the future). Similarly, the term “print media” as used herein is intended to represent all forms of materials onto which markings may be transferred, including paper, transparencies, card stock, cardboard, metals, alloys, woods, ceramics, etc. (whether currently known or developed in the future).
Some electrostatic printing systems use a roller or magnetic brush to load toner onto a donor roll, which delivers the toner to the latent charge image on the photoreceptor. After the toner is stripped from the donor roll and delivered to the image, the donor roll reloads toner from the magnetic brush. In order to maintain consistent printing quality, various properties of the toner should be tightly controlled including the concentration of toner particles relative to carrier granules (or other similar development material) within the mixture of toner particles and carrier granules. This measure commonly referred to as “toner concentration” or TC.
Various devices are utilized to detect toner concentration including optical devices and electronic devices. In one example of an electronic device that detects toner concentration, a first voltage can be applied to a developer carrying member and a second voltage can be applied to a metering blade. The current between the developer carrying member and the metering blade is measured, generating a signal indicative thereof, and the toner concentration is calculated as a function of the generated signal. In another example, infrared densitometers (IRDs) can be used to measure toner concentration (TC) based on density.
In addition, there are several existing methods to calibrate TC sensors (empirically testing the TC sensors with a fresh package of toner/developer mixture, using a vacuum tool to remove a limited portion of the toner/developer mixture and independently empirically testing the toner/developer mixture, etc.) These methods can be time consuming and inaccurate. If the TC sensor is incorrectly calibrated, image quality defects can occur. If the TC is too low, reload can occur, and if the TC is too high, background, spitting and emissions can occur. The actual TC percentage is not as notable as avoiding the image quality defects that result when TC is simply too low or too high.